Murphy's Law and karma are almost similar and related to each other...
picture this what goes up must come down unless youre a bird and know how to fall with grace.... but still, if the bird took a shit while in flight it must come down(Murphy's Law). now Karma - for every action there is a reaction - same as being angry and taking a walk where that bird is......well I'll cut to the point. its a great possibility to be very angry in a park. and for some reason a bird happens to shit on you while flying... now thats karma and Murphy's law

What do I think when I hear it? I think that it isn't true -- at least not directly as most people understand it.

And philosophically I KNOW it isn't true from experience. One friend gives a little more than another. One lover loves a little more than the other. One person spends a little more on another. Good deeds go ignored, evil deeds go unpunished. The notion that "equal and opposite reaction" applies to life as well as physics is just outright incorrect. That sounds like something a stoned, conservative christian highschool guidance counselor would put on a motivational poster.

"for every action there is an equal and opposite reaction" is more of an expression to track the movement and conversions of energy. If I apply 2 pounds of pressure on a counter with my finger, both the counter and my finger tip experience that pressure. If I throw a ball, there is a force on the palm of my hand as well as the ball. Energy cannot be destroyed so it all has to go somewhere, but if for every action there were a literal equal and opposite reaction, the universe would be completely static.

BearSolwrote:
So I don't think that rule applies to life in general, just physics, unless you're Christian, then God bonded those molecules and made that water boil.

As a Christian and an engineer, I'm sort of curious what you mean by that?

I mean, I do believe that the universe was created with intent, so God did create the fundamental rules that undergird physics, say. But what'cha mean?

I mean, "If I tell most Christians..." You can read the entire comment in the context in which it was started. Which means, not to say that all Christians are this way, but in 'Murica, most of the overly vocal ones I've run across aren't as 'modern' in their Christianity.